Power amplifiers are commonly used to amplify electrical signals supplying power to certain types of electronic devices, such as audio speakers. Most power amplifiers use, and depend upon, clean, regulated direct current (DC) power input. Unregulated DC power generated from unregulated alternating current (AC) is “noisy”, containing power fluctuations unsuitable for most power amplifying applications.
In typical applications, power amplifiers must convert an unregulated, noisy 120-volt AC power source into a regulated, clean DC power source. If the unregulated AC power input is simply rectified to a DC power input, any fluctuations, noise or ripple in the AC power signal may be transferred to the DC power signal. The noise inherent in DC power in this situation may be translated to the amplified output signal. In audio applications, such excessive variances in the power supply will result in undesirable hum, distortions, and noise at the speaker. As such, there is a need for regulated DC power supplies to power applications with a reduced noise factor.
Conventional power amplifiers rectify an AC power source to a regulated DC power source with transformers and other active inductive and capacitive circuits, which account for the majority of the weight, waste heat output, and cost of production associated with these prior-art amplifiers. As such, there is also a need for audio amplifiers that weigh less, produce less heat, and cost less.
A number of approaches have been tried to minimize or overcome the above-identified problems. U.S. Pat. No. 4,042,890 to Eckerie filters the DC power signal to reduce high-frequency noise. U.S. Pat. No. 4,605,910 to Covill produces a switch modulated signal for producing an output signal that is independent of the supply voltage, thereby eliminating noise caused by fluctuating AC voltage signals. U.S. Pat. No. 4,737,731 to Swanson senses variations in the DC power signal and adjusts the gain in the audio frequency signal according to the variances to reduce modulation distortion. In U.S. Pat. No. 5,132,637 also to Swanson, a plurality of actuable power amplifiers are controlled by a correction signal to produce a cleaner signal. U.S. Pat. No. 5,777,519 to Simopoulos uses a correction signal as an input to a variable switching power supply to eliminate some noise in the power signal.
However, each of these methods share the problems of high cost, high heat loss, high weight, and overall inefficiency. A different method for regulating the power output that eliminates the regulated DC power source would offer significant advantages in cost and efficiency as well as a significant reduction in weight and increase in output power.